Self-assembly of TiO 2 /ZIF-8 nanocomposites for varied photocatalytic CO 2 reduction with H 2 O vapor induced by different synthetic methods.

Photoreduction of carbon dioxide (CO ₂ ) provides an effective perspective for solving the energy crisis and environmental problems. Herein, two types of composite photocatalysts (TiO ₂ /ZIF-8) based on ZIF-8 and TiO ₂ have been designed and synthesized with the help of the grinding method and the solid-synthesis method. Both composite photocatalysts are employed for the photocatalytic reduction of CO ₂ . In composite photocatalysts prepared by the grinding method, ZIF-8 particles are distributed on the surface of TiO ₂ , and provide extra available spaces for storing CO ₂ , which is beneficial for improving their photoreduction performances. As a result, an enhanced CO formation rate of 21.74 μmol g ^-1 h ^-1 with a high selectivity of 99% is obtained for this family of composite photocatalysts via the solid-gas mode without photosensitizers and sacrificial agents. For comparison, the other family of composite photocatalysts synthesized via the solid-synthesis method possesses structures similar to ZIF-8, where TiO ₂ is encapsulated inside the framework of ZIF-8. This structural feature obstructs the contact between the active sites of TiO ₂ and CO ₂ , and leads to lower activities. The best CO formation rate of this family is only 10.67 μmol g ^-1 h ^-1 with 90% selectivity. Both the structural features of the two families of photocatalysts are described to explain their differences in photoreduction performances. The experimental finding reveals that different synthetic approaches indeed result in diversified structures and varied photocatalytic performances. This work affords a new scalable and efficient approach for the rational design of efficient photocatalysts in the area of artificial photosynthesis.
Competing Interests: There are no conflicts to declare.
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